1. Field of the Invention
The present invention relates to a write control method and apparatus associated with a hard disk drive (HDD). More particularly, the invention relates to a write control method for a HDD performing a synchronous write head retraction upon detection of a free fall state.
This application claims the benefit of Korean Patent Application No. 10-2006-0058100, filed on Jun. 27, 2006, the disclosure of which is hereby incorporated by reference.
2. Description of the Related Art
An HDD is a recording device used to store information. Information is recorded on concentric tracks on the surface of a magnetic disk. The disk is mounted on a rotating spindle motor, and the information is accessed by a read/write head mounted on an actuator arm rotated by a voice coil motor (VCM). An electrical current supplied to the VCM generates torque that moves the read/write head over the surface of the disk. The read head reads recorded information by sensing variations in a magnetic field associated with the surface of the disk. A variable current is supplied to the write head to record information on the tracks. This current generates a magnetic field that selectively magnetizes the disk surface in relation to the information being recorded.
The contemporary incorporation of HDDs into a range of consumer products as resulted in continuing efforts to miniaturize HDD designs. Indeed, some HDDs are now being used in portable mobile devices such as laptop computers, MP3 players, cellular phones, and personal digital assistants (PDAs).
Unfortunately, portable mobile devices are prone to being dropped during their use. The resulting mechanical shock can be particularly devastating to HDD components (e.g., read/write heads, associated transport mechanisms and disk surfaces), since conventional HDD designs make no provision whatsoever for such abuse.
To better secure (or immunize) miniaturized HDD components from mechanical shocks, technology has been introduced to detect external impacts (e.g., drops, vibration or other shocks), and if necessary, unload the read/write head in the HDD. In this context, the term “unload” generally subsumes any process whereby a read/write head is moved from a normal range of operating positions into a specially provided shock resistant position.
Examples of technology adapted to protect a HDD from external impacts are Japanese Patent No. 2000-99182, published in Apr. 7, 1999, and Japanese Patent No. 2002-8336, published in Jan. 11, 2002. These applications generally describe technology that detects a so-called “free fall state” commonly associated with drops. A free fall sensor (FFS) is used to detect the free fall state. In response to this detection, the read/write head is quickly unloaded.
FIG. 1 is a perspective view of a conventional FFS 50 formed from a 3-axis acceleration detector. FFS 50 includes a suspended mass 52 and attached, orthogonally disposed piezo elements 54. In its suspended configuration, mass 52 moves in the x, y, and z-axis directions under the influence of external forces (e.g. gravity) applied to a HDD incorporating FFS 50. Movements in the position of mass 52 stress (compressive or tensile) the suspending attachments and induce changes in the amplitude of electrical signals output by piezo elements 54. Motion or acceleration of mass 52 in the x, y, and z-axis directions may be determined in relation to the electrical signals output from piezo elements 54. A free fall state for the HDD may then be detected using the calculated acceleration of mass 52.
FIG. 2 is a conceptual diagram and FIG. 3 is a related waveform diagram further illustrating the conventional approach to detecting a HDD free-fail state. Referring to FIG. 2, free fall acceleration is applied to a HDD when it is dropped at time t=0. The HDD is in a free fall state during a time period t=1 until striking a surface at time t=2. Before being dropped at time t=0, a free fall sensor within the HDD detects a constantly applied acceleration of “1G” or the unit gravity acceleration constant. However, while falling during time period t=1, the free fall sensor no longer detects the 1G acceleration upon its constituent mass. This detection transition from a 1G applied force to a 0G applied force indicates the free fall state.
With reference to FIG. 3, a 3-axis summed acceleration vector is constantly calculated from electrical signals provide by the free fall sensor. So long as the HDD remains in a held or supported state, this acceleration vector remains close to 1G. Once the HDD is dropped however, the acceleration vector falls to 0G passing through a threshold Th during a fall time period Tfall. As illustrated in FIG. 3, the free fall state is detected and a corresponding “DETECT FFS” is generated in relation to this signal transition. When the free fall detection signal “DETECT FFS” is generated (here a logic value of “1” is assumed), the HDD performs an unload operation. The unload operation generally involves retracting the read/write head from its normal operating range and then parking the read/write head in a secure location away from the surface of the disk.
A conventional HDD initiates the unload operation upon detection of a free fall state in order to quickly protect the HDD components. FIG. 4 is a flowchart illustrating a conventional unload operation in a case where a free fall state occurs while the HDD is conducting a write operation.
Referring to FIG. 4, an HDD initiates a write operation (i.e., enters a write mode) in response to an instruction received from a host (not shown).
When in write mode, the HDD positions its read/write head over a target sector of a target track of a disk, and then writes data to the target sector (S404). The HDD also writes data sector by sector. This write operation performance is well understood.
While in write mode and while performing one or a sequence of write operations, the HDD determines whether or not a free fall state is detected (S406). In the illustrated example, a free fall detection signal acts as an interrupt signal to the normal write mode operation of the HDD.
So long as a free fall state is not detected (S406=no), the HDD determines whether or not the write operation is complete (S408). If it is determined that all pending write operations are complete (S408=yes), the write mode is terminated. Otherwise (S408=no), the write mode persists and write operations are performed (S404).
However, when a free fall state is detected (S406=yes), the HDD immediately stops the write operation (S410) and performs an unload operation (S412). The unload operation moves the read/write head to a safe parking area (e.g. a parking ramp or off the recording surface of the disk).
The HDD then waits until the free fall state ends (S414). Once the end of the free fall state is sensed (S414=yes), the HDD loads the read/write head back into its working condition (S416), and restarts the interrupted write operation (S418). The end of the free fall state is typically determined by detecting the passing of the mechanical shock that is inevitably associated with the free fall state. A shock detection sensor (not shown) may be used for this purpose.
However, according to the conventional unload operation illustrated in FIG. 4, if the HDD is reset in response to the free fall state induced shock, a read error may occur in the sector being written to when the free fall state caused an interrupt in operation.
Consider, for example, the conceptual diagram of FIG. 5 which further illustrated how such a read error might be generated by use of the conventional unload operation.
Referring to FIG. 5, it is assumed that a write operation is performed in the order of a sector N, a sector N+1, and a sector N+2. According to the conventional unload operation, as soon as a free fall state is detected, the write operation is stopped and the unload operation begins.
For example, if the free fall state is detected while the write operation is writing data to sector N+1, the write operation immediately stops, and the unload operation is performed. Thus, data may not be completely in sector N+1 and will not be written to any subsequent sector (i.e., sector N+2).
So long as the write operation is performed for all of sector N+1 after the free fall state ends, no read error will occur during future read operations. However, if shock associated with the free fall is severe that the host device or HDD enter a reset state, the information associated with the interrupted write mode will be lost and the ongoing write mode is cancelled. Thus, when the HDD ultimately resets in its operation, even though the HDD has survived the drop and the corresponding free fall state has ended, the data associated with the interrupted write operation is not written to sector N+1. Accordingly, sector N+1 may include partially written and erroneous data that will cause a read error during subsequent read operations.